Reuters reported that Rio Tinto said that it knew of no basis for speculation over a bid for the company by rival miner BHP Billiton.

Rio was responding to an enquiry from the Australian Stock Exchange after its shares rose 5.4% on Wednesday, bucking a downtrend in the wider market.

Rio's shares rose, swept up by rumors ranging from a sweetened cash bid by BHP Billiton to a Chinese counter bid. Speculation had swirled in the Australian market that Rio may be considering softening its opposition to BHP's current all share offer.